The present invention relates to a transmission system for use in communicating with a mobile station.
A variety of mobile communication systems, such as a mobile telephone or portable telephone for communicating with a mobile station have heretofore been put into practice. The mobile communication system is fundamentally the same communication system is that for communicating with fixed stations.
A reception signal received at a mobile communication terminal, such as mobile telephone or portable telephone tends to be distorted due to the influence of multipath fading. Specifically, when the multipath fading occurs, a propagation delay between paths increases to cause an intersymbol interference. As a consequence, preceding and succeeding codes overlap each other to deteriorate a transmission characteristic.
In order to satisfactorily receive a reception signal even when the transmission characteristic is degraded, a sync (synchronizing) detecting circuit formed of an adaptive equalizer or a PLL (phase-locked loop) circuit has to be applied so that a receiver becomes complex in arrangement and expensive.
Furthermore, when a modulated waveform to be transmitted is changed with a probability distribution which is often referred to as a Gaussian distribution, a peak-to-peak value takes a large amplitude so that a signal transmitted via a transmission amplifier or the like is distorted and a spectrum of a modulated wave is widened to exert an adverse influence on the adjacent channel.
In view of the aforesaid aspect, it is an object of the present invention to provide a communication system which can satisfactorily communicate with mobile stations by a transmitter and receiver of a simple arrangement.
According to a first aspect of the present invention, there is provided a communication system which is comprised of transmission processing means for transmitting a plurality of carriers having different frequencies simultaneously and transmitting data on the basis of a phase difference between the carriers.
According to a second aspect of the present invention, there is provided a communication system which is comprised of modulating means for outputting a modulated output waveform in which an amplitude probability distribution is approximate to a Gaussian distribution, a limiter for amplitude-limiting an output waveform of the modulating means, and a filter for filtering out an output of the limiter, wherein the limiter amplitude-limits the mixed signal at a rate of about 1.5 times of standard deviation of amplitude distribution or greater and an output of the filter is transmitted.
According to a third aspect of the present invention, there is provided a communication system which is comprised of means for transmitting a plurality of carriers having different frequencies simultaneously, wherein a predetermined time waveform is multiplied with each of carriers.
According to a fourth aspect of the present invention, there is provided a communication system wherein signals are phase-modulated by a plurality of carriers having different frequencies and transmitted simultaneously. The communication system is comprised of carrier generating means for generating carriers and transmitting means for supplying phase values to the carrier generating means as initial phase values and sequentially adding phase values to the carriers at every sample interval to directly obtain data modulated into carriers.